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This is the first part in a series I'm doing on designations of aircraft that should have been, but were not, for whatever reason. Conveniently, the first three happen back-to-back-to-back in the U.S. fighter series. The first one is arguably the most successful in terms of aircraft produced.
If you've never heard of the Republic F-96, that's okay. The fact is that the Republic F-84F Thunderstreak, arguably the most successful variant of the venerable F-84, initially had - and should always have carried - an entirely new designation. Ironically, the initial F-96 prototype had a lot more in common with its straight-winged forebears than it did with the swept-wing machines it presaged.

Almost as soon as the first Republic XP-84 Thunderjet made its initial flight on February 28, 1946, Alexander Kartveli and the team at Republic knew it was outdated.

Data recovered from captured research facilities and scientists in Nazi Germany at the end of World War II indicated that designers there found advantages from swept-back wings, particularly at high speed. With the F-84B already in production by late 1947, Republic were now having to scramble to save the straight-winged Thunderjet from a short service life.

Republic YF-96A Thunderstreak

Republic developed several variants of the F-84 with various aerodynamic and propulsion upgrades in desperate attempts to keep the Thunderjet project alive for the USAF. However, by 1949, it was clear that a swept-wing aircraft would have to be developed if republic were to remain competitive with the likes of North American with their F-86, McDonnell's F-88, and Lockheed's F-90 - all of which employed swept wings.

Alexander Kartveli approached the problem from the simplest angle possible: Take a standard F-84E fuselage, and attach 38.5-degree swept wings and tailplane. This approach was an efficient one - It enabled quicker production due to not having to re-tool the factory (the new plane would have 55% commonality with the F-84E), and permitted the possibility of modifying existing straight-wing machines to the new standard.

As is custom, the Air Force provided Republic with a new designation for the aircraft - F-96. Republic dubbed it 'Thunderstreak.' The first was ready for flight in June of 1950.

The YF-96A, s/n 49-2430, made its maiden flight on June 3rd, 1950. Performance turned out not to be up to the levels Republic was hoping for. The YF-96A topped out at 693 mph, while the straight-winged F-84E had a top speed of 613 mph. In addition, like its predecessor, the YF-96A's performance died as it climbed, with a ceiling under 40,000 feet. Compared to the F-86 Sabre, which was capable of breaking the sound barrier in a dive, the F-96 looked headed for cancellation.

Then, on June 25th, 1950, everything changed. On that day, North Korea invaded South Korea, and the Korean War was on. With it came drastically expanded military funding, which had floundered in the draw-down after World War II. And with it, the YF-96 had new life, if its technical shortcomings could be solved.

The main drawback was the engine. The YF-96A was powered by the same Allison J35 engine as the F-84E. The swept surfaces did allow for some additional speed, but to reach the heights hoped for, the type needed a more powerful engine.

The Air Force asked Wright Aeronautical to build the British Armstrong-Siddely Sapphire turbojet engine under license in the U.S., under the designation J65. this engine, which already powered the Gloster Javelin and Hawker Hunter, could crank out more than 7,000 pounds of thrust, compared to the J35's 5,500 pounds. This new engine would be installed in the new Thunderstreak.

But there was a problem. The J65 was slightly larger than the J35, and required a greater volume of air than the F-96's circular nose intake could provide. The lack of air to the engine resulted in drastically inferior power and performance, despite the type's first flight with it in February 1951. So Republic had to go back to the drawing board. Kartveli's solution was to add a seven-inch length-wise plug into the fuselage, giving it a fatter, ovular cross-section.

As a result, most of the tools that Republic hoped to re-use to build F-96s would have to be tossed out, resulting in massive production delays. Consequently, the commonality factor with the straight-winged F-84s was dramatically reduced from 55% to just 15%. Two more prototypes were ordered, each with its own revised design to accommodate the new power plant.

Re-designation to YF-84F

By now, Congress was getting impatient with the F-96 program. It had staved off cancellation with the outbreak of the Korean War, but enthusiasm still waned. So Kartveli decided to play salesman.

He submitted to the Air Force that the XF-96A be re-designated YF-84F, hoping that selling Congress that this was a new sub-type of an existing aircraft would be more palatable than buying a completely new aircraft, despite the fact that the new type was only 15% similar to its predecessors. Congress fell for it, and the Thunderstreak was ordered into production as the F-84F.

In the meantime, Republic also pitched and got an order for an improved straight-win F-84 variant, the F-84G, to be produced quickly while the F-84F was ironed out. More than 3,000 F-84Gs would roll off the line at Republic - the most of any F-84 model.

The first YF-84F, s/n 51-1344, with its ovular cross-section, was flying by the end of 1951.

The second YF-84F, s/n 51-1345, represented a radical redesign. Instead of the nose intake, this machine was completed with wing root-extension intakes and a needle nose. However, the new intakes did not allow enough air to get to the engine as was needed, and power losses were dramatic compared to the nose-intake model. So the F-84F would go into production with a nose intake.

However, at this time, the Air Force was looking for a swept-wing upgrade from its straight-winged Lockheed RF-80 Shooting Star reconnaissance aircraft. Although the F-84F had lackluster performance for a fighter at high altitude, its low-level performance was rock solid in ground attack roles, and by inference, the type would make an excellent choice for low-level reconnaissance.

YRF-84F Thunderflash

The solid-nosed variant also permitted the installation of cameras. So a new prototype was ordered, s/n 51-1828, with an enlarged, aardvark-esque nose section to accommodate camera packages. The first pre-production YRF-84F flew for the first time in February 1952.

YF-84J Thunderstreak

Republic attempted one last push with the F-84F design in its YF-84J. The F's fuselage was enlarged once again, along with the nose intake, to accommodate the General Electric J73 engine, which produced a maximum of 9,500 pounds of thrust. This development finally achieved the performance that Kartveli had envisioned for his swept-wing fighter, as one YF-84J broke the sound barrier in level flight in April of 1954. But the cost of converting the existing F-84Fs to F-84J standard, coupled with the coming emergence of the Century Series fighters like the North American F-100 Super Sabre, spelled the end of the F-84J project.

FICON Prototype

There was one last task for the original YF-96A prototype to undertake. In preparation for the FICON project, 49-2430 was modified with aerial coupling gear and a drooped horizontal stabilizer in order to be mated with a B-36 mother plane to test the concept. The tests with the B-36 proved that the system could indeed work for roles including aerial reconnaissance and even nuclear strike. 25 RF-84Fs were ordered to be converted to RF-84K standards, with coupling gear and anhedraled tailplanes, to be paired with 10 modified GRB-36D mother ships. After service with SAC's 99th Strategic Reconaissance Wing (B-36s) and 91st Strategic Reconnaissance Squadron, the project was suddenly abandoned in April of 1956. While the difficulties in operating parasite aircraft operationally were unquestionably a factor, it should also be noted that the U-2 spy plane entered service with the CIA and SAC in January of that same year.

The original YF-96A (described as the YRF-84F FICON) sits on display in the Research and Development Galler at the National Museum of the United States Air Force in Dayton, Ohio. It is the only one of the swept-wing F-84 prototypes to still exist. All the others have been scrapped.

Ultimately, given how much of a departure it was from the original F-84, the F-84F probably should have kept its original F-96 designation. Indeed, the original prototype's sleek form represents the highest refinement of aesthetics for a plane that had the unflattering nickname of 'Groundhog.'

Should-have-been equivalent designations:

F-84F - F-96A (21 different sub-types)

RF-84F - RF-96B

YF-84J - YF-96C

RF-84K - RF-96D

XF-84H - XF-96E

But Alexander Kartveli's decision to fold the plane's number in with the original type likely enabled it to become the great plane that it was, rather than being relegated to history's boneyard. It was a bold and cunning decision, but one that surely helped keep him, and Republic itself, in good stead with Air Force leaders heading into the mid-1950s, and the development of the F-105, which would prove troublesome. In this respect, Kartveli's genius as a businessman, in addition to a designer, cannot be overlooked.